1. Field of the Invention
The present invention generally relates to structures of magnetic circuit systems, more particularly to an external-magnet-type magnetic circuit system.
2. Related Art of the Invention
Generally, transducers, such as speakers, need a magnetic circuit system for generating electro-magnetic force to drive a coil to move.
Typically, the magnetic circuit system includes a T-shaped yoke having a center pole projecting from a center part of a plate, a ring-shaped magnet positioned on the yoke, and a ring-shaped top plate attached to the magnet. A magnetic gap is formed between the center pole and an inner surface of the top plate. If a coil is suspended in the magnetic gap, when electrified, the coil will be given a magnetizing force F, and the force F is determined by the product of magnetic flux (B), displacement of the coil (L), and current applied on the coil (I). Production of B and L is called magnetizing force factor. If the magnetizing force factor is not even during the vibration of the coil, the magnetizing force will lead to non-linear distortion.
So, it is necessary to provide an improved magnetic circuit system for solving the problem mentioned above.